What is a planetary nebula?

1 Answer

The gas cloud puffed out from red giant stars at end of their life.

Explanation:

When most of hydrogen is burned the gravity of the star become less..Star become red giant. pressure and temperature from helium burning push out the gases and gravity is weak so star become red giant.Then the outer layers are puffed put for a gas cloud around star..THis gas cloud is,called planetary nebula.